As part of a continuing study on canine atherosclerosis we propose: 1) to investigate changes in the retinal vasculature of dogs maintained on a standard atherogenic regimen to determine if the dog has retinal atherosclerosis as seen in man. 2) to correlate the type and severity of retinal vascular lesions with those produced in the cerebral and large systemic arteries. 3) to relate the vascular lesions to blood cholesterol, cholesterol esters, triglycerides, phospholipids and lipoprotein levels. We intend to answer the two questions: 1. Does the canine retinal vasculature respond as that in man to generalized atherosclerosis (indications for this already exist - see A-2 Background). 2. Does the eye provide a window into the vascular system through which the observer may obtain an estimate of the severity of the generalized atherosclerosis. The basic study will utilize the eyes from the foxhounds currently being investigated under NIH Contract No 1-HI-4-2903. Additional groups of dogs will be used as controls for total thyroidectomy (used in contract foxhounds) and 12 month atherogenic diet feeding (contract foxhounds are fed for 6 months on atherogenic diet). Specific methodology for the retinal vasculature study will entail: the comparison of normal and treated eyes by routine ophthalmoscopy, fundus photograph, mural cell: endothelial cell counts on digested retinas, paraffin ad frozen sections and electron microscopy.